This invention relates to control of the inflation of tandem, inflatable formation packers disposed on a string of casing in a well bore which traverses earth formations, and more particularly, to a system for sequentially actuating tandem arranged inflatable formation packers so that the packers are inflated in a sequence from the bottom packer upwardly in a well bore.
In completion of oil wells, one completion system involves the use of a number of inflatable formation packers disposed lengthwise along a string of casing disposed in a well bore. In operation, the supporting casing is filled with fluid as is the annulus between the packers and casing and the well bore. When it is desired to inflate the formation packers, pressure is supplied through the fluid in a casing which acts upon an enclosed internal space of the formation packers and expands them radially outward into contact with the wall of the well bore. Obviously, when the inflatable packers expand, the fluid that originally occupies the annular volume between the packers and well bore is displaced. The displacement of the fluid in the annular volume may (1) move upwardly to displace fluid upwardly in the casing well bore annulus, (2) move downwardly and enter permeable intervals between the packers, (3) enter permeable intervals adjacent to or between the packers, (4) initiate and flow into fractures adjacent to, between or below the packers, and/or, (5) become trapped in borehole irregularities preventing complete inflation of the packers. Only movement of the fluid upwardly in the annulus is desirable as the interaction of trapped fluids with the borehole adversely affects the formations and operation of the packers.
Heretofore, there has been no effective control of the packer inflation where multiple packers are utilized. For example, inflation of the top packer first can form a flow restriction that completely prevents upward movement of the displaced fluid. Random inflation of the packers traps annular fluid along the packers if they inflate at different rates.
Thus, the purpose of the present invention is to inflate the packers in a predetermined manner so that upward movement of the fluid in the annulus between the borehole and the packer or casing occurs first at the lowermost inflatable packer and by sequentially inflating the packers in an upward direction thereby facilitating a complete unhampered inflation of the packers and upward flow of fluid and thereby minimizing the risk of well damage by virtue of trapped fluid.
Heretofore, it has been proposed to obtain sequential inflation of packers by sequential operation of pressure differentially actuated valves disposed in tandem packers where the pressure operated valves are set to open sequentially in response to pressure beginning with the lowermost packer first. This pressure responsive system has application under certain downhole conditions. In many instances, however, downhole pressure, under normal operating conditions, cannot be directly monitored at the surface and data from the surface pressure measuring devices must be combined with the expected hydrostatic pressures to estimate the pressure that is acting on a given valve at a given depth within the well bore. Thus, there is considerable room for inaccuracy in this system and errors resulting from inaccurate surface readings and/or unexpected hydrostatic forces often exceed the margin of error. That is, the error in the actual pressure exceeds the difference between the pressure settings of pressure operated valves in different packers resulting in the simultaneous opening of two or more pressure valves in two or more packers and the resulting failure of the packer system to sequentially operate. Also, in some cases the number of packers that may be run in tandem in a well bore is limited because the pressure differential required to open the valve in uppermost packer cannot be effectively attained in the casing.